Most vehicles in operation today are powered by internal combustion (IC) engines. Internal combustion engines typically have a plurality of cylinders or other working chambers where combustion occurs. Under normal driving conditions, the torque generated by an internal combustion engine needs to vary over a wide range in order to meet the operational demands of the driver. Over the years, a number of methods of controlling internal combustion engine torque have been proposed and utilized. Some such approaches contemplate varying the effective displacement of the engine. In conventional variable displacement engine operation, a fixed set of cylinders are deactivated during low-load operating conditions. For example, an eight cylinder engine may fire all eight cylinders, then drop to a four cylinder mode (in which four cylinders are fired and four are deactivated). Cylinder deactivation during low-load operating conditions can help reduce fuel consumption.
While the above approaches work well for various applications, there are ongoing efforts to further improve the fuel efficiency and performance of variable displacement engines.